Variable inductance device



Dec. 27, 1938. A w 2,141,890

VARIABLE INDUCTANCE DEVICE Filed June 195s o\\: Mu

INVENTOR ADOL was A'ETORNEY Patented Dec. 27, 1938 UNITED STATES VARIABLE INDUCTANCE DEVICE Adolf Weis, Berlin-Charlottenburg, Germany, as-

signor to Siemens & Halske, Aktiengesellschaft, Berlin- Siemensstadt, Germany, a corporation of Germany Application June 6, 1936, Serial No. 83,892 In Germany July 26, 1935 1 Claim.

of high-frequency coils comprising a telescoping or shiftable core of magnetizable material of the kind known as dust-cores, that the factor when introducing the core into the coil is altered, to be more precise, becomes greater. While the quality or merit figure g if the factor 25 stayed constant, as compared, for instance, with the frequency of 500 kc., should rise to a value three times higher at 1500 kc., it has been observed in practice that a decrease rather than an increase takes place. However, this tends to prove an the accuracy of the observation above mentioned. The cause underlying this fact may be sought in that apparently the losses in the core material and in the coil or winding, in the presence of high frequencies, relative to the inductance value 35 to which the variometer has been set, are essentially higher than in the presence of lower frequencies, with the consequence that an increase in the factor is occasioned.

Investigation on this subject has shown that the problem may be solved by artificially raising the losses in the magnetizable core gradually as 46 the core is introduced into the coil. This may be done by raising the iron content of the core or by using a coarser iron powder, or by reducing the insulation between constituent iron particles.

However, these steps and means are difiicult to 50 carry into actual practice because in large-scale manufacture of cores, say, by pressing and molding, it would be rather hard to obtain at a given place a higher content of iron than at other places, or to insure a similar result in reference 56 to the distribution of the insulation material.

One solution of the problem that is conceivable would consist in that the core is composed of different strata or layers, each of which would have an average content of iron and insulation material which would differ from one layer to an- 5 other layer. Quite apart from such gradation, the cost of production oi. the variometer would be considerably increased on the ground that the different parts of the core would haveto be made separately before assembly.

Another method would be to make the core along the direction of its shift into the coil with a cross-section growing gradually towards its end. However, this involves a considerable growth in the size of the coils and the dimensions of the core, and this means that the advantage residing in variometers provided with dust-cores, that is to say, reduced size, is lost. On the other hand, the increase in core material resulting from the increase in cross-section in itself is not sufficient to produce the requisite growth in the losses.

In the drawing, Figure 1 illustrates one form of the invention wherein the coil is surrounded by a shield; Figure 2 illustrates a cross section 26 through an embodiment of the invention wherein a tapered type core is used; and, Figure 3 is an elevation of the device shown in Figure 2.

Contradistinct to these conceivable ways and means as just discussed, the invention discloses 80 an essentially more advantageous solution which consists in that the core of magnetizable material the outside may be enveloped by a shield 3 consisting of magnetizable material resembling dust-core material. This shield precludes stray or leakage of the coil liable to act upon neighboring circuit elements, for instance, when built into a broadcast apparatus. On the other hand, however, it prevents the penetration into the coil of stray or extraneous fields originating from other circuit parts such as neighboring air-core coils or transformers.

The core made of magnetizable material similar to dust-core material adapted and designed to be telescoped or shifted into the coil winding 2 and effecting the tuning of the variometer is indicated by 4. As also shown in the drawing quite clearly the same has a metallic insert 5 in the form of a pointed cone whose base is located at the end of the core which is shifted into the interior of the coil only when the variometer is tuned to lower frequencies; in other words, in the presence of lower frequencies the compact mass of metal introduced into the field of the coil, to raise the losses, is essentially greater than in-the high-frequency ranges. whence there results a constant value and thus the intended shape of the quality values Another embodiment is shown in Fig. 2, Fig. 3 being an elevation of Fig. 2. In this case the variometer consists of a stationary E-shaped core 6 of magnetizable material whose recesses I enclosed between the limbs or legs 0 are designed to accommodate the adjustable coil winding 8 which, according to the desired tuning, is adapted to be introduced to varying depths into the recesses I. In order to insure suiilcient increase in the inductance of the coil toward the end of the recesses 1, the core 6 presents a gradually growing cross-sectional area. This is clearly shown in Fig. 2. However, as pointed out before, this step alone is not suiiicient to insure at the same time the requisite increase of the losses. In fact, for this purpose, in the core part entirely accommodating the coil winding at low frequency, in analogy with the form or construction illustrated in Fig. 1, a conical metal pin is embedded which has its maximum diameter at this end 0! the core. The effect of this arrangement, as to the rest, is the same as Fig. 1.

In conjunction with the coil winding is provided an adjustable yoke III which is also made from magnetic material of the kind used in dust-cores, though having preferably a permeability which is 2,141,soo

higher than that oi-the core I. The yoke ll prevents a reduction 01 the maximum permeability existing in the core 0 as a result oi the air-gap otherwise present in this kind oi core. so that the permeability oi the core can be largely utilised. Moreover, owing to the fact that it varies the cross-section of the magnetisable core at one point in the magnetic circuit or path, it contributes to the adjustment of the inductance.

The inserts or embedded means here disclosed. may, as to the rest, be used in connection with all other types of core employed and customary in high-frequency variometers.

I claim:

An inductance device comprising a coil provided with a core composed of compressed finely divided magnetic material, said core being E-shaped in cross section and arranged so that the tree limbs thereof are tapered toward the outer ends so as to terminate in a narrow edge, movable mounting means for the coil comprising a sleeveshaped member arranged so as to be capable of being inserted completely within the spaces between the i'ree limbs 01 the core, said sleeveshaped member having a coil supporting portion and a portion composed of magnetic material, said core being provided with a conical insert composed of solid high conductive metallic material positioned within the central limb oi the core so that the small end of the insert is toward the narrow edge of the core and so that its axis coincides substantially with the axis of the sleeve member.

ADOLF WEIS. 

